Fuel cell compressor system

ABSTRACT

The invention provides a fuel cell compressor system that comprises a motor, including a motor shaft driven by the motor; a drive housing at least partially surrounding the motor shaft; a first gear set driven by the motor shaft; a carrier torque tube driven by the first gear set; and an impeller. The impeller includes an impeller shaft driven by the second gear set, so that the impeller shaft is configured to rotate at a speed greater than motor speed. Embodiments of the invention may also include a first bearing supporting the carrier torque tube and a second bearing supporting the impeller shaft. Embodiments of the invention may also include a seal system.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Nonprovisional patentapplication Ser. No. 11/609,650, filed Dec. 12, 2006, now pending, whichclaims the benefit of U.S. Provisional Patent Application No.60/750,225, filed Dec. 14, 2005, both of which are hereby incorporatedby reference in their entirety.

BACKGROUND OF INVENTION

a. Field of Invention

The invention relates generally to a fuel cell compressor system,including a fuel cell compressor system that uses a gear set configuredto drive an impeller at a speed greater than motor speed.

b. Description of Related Art

Fuel cells generally require clean, pressurized fluid to operatereliably. Centrifugal compressors designed for low flow, operate moreefficiently at higher speeds. Accordingly, conventional centrifugal fuelcell compressors are typically directly driven by high-speed motors.However, the use of high-speed motors can involve some disadvantages.Among other things, sealed, greased bearings are commonly unable toadequately operate at such higher motor speeds. Also, while open oilbearings may operate at higher compressor speeds, their use requiresinefficient, complex, oil lubrication systems to survive. Further, whileair bearings can sometimes be used in higher-speed environments, andoperate cleanly, such bearings are often expensive and impractical formass production.

Consequently, there is a desire for a fuel cell compressor system thatcan operate with a low-speed motor, while retaining a sufficiently highcompressor speed for efficient, reliable fuel cell operation. Further,there is a desire for a fuel cell compressor system that may beconfigured for operation with standard mass produced bearings that areotherwise typically not usable in connection with high-speed compressoroperation.

SUMMARY OF INVENTION

In an embodiment, the invention provides a fuel cell compressor systemthat comprises a motor, including a motor shaft driven by the motor; adrive housing at least partially surrounding the motor shaft; a firstgear set driven by the motor shaft; a carrier torque tube driven by thefirst gear set; and an impeller. The impeller includes an impeller shaftdriven by the second gear set, so that the impeller shaft is configuredso as to be capable of rotating (or spinning) at a speed (i.e.,rotational speed) that is greater than motor speed. Embodiments of theinvention may also be used with a multi-stage compressor that allows,for example, first and second impellers to rotate at different speeds.

Various features of this invention will become apparent to those skilledin the art from the following detailed description, which illustratesembodiments and features of this invention by way of non-limitingexample.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example,with reference to the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a fuel cell compressor system inaccordance with an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of a fuel cell compressorsystem in accordance with another embodiment of the present invention.

FIG. 2A is a partial cross-sectional view of a fuel cell compressorsystem in accordance with another embodiment of the present invention.

FIG. 2B is a partial cross-sectional view of a fuel cell compressorsystem in accordance with another embodiment of the present invention.

FIG. 3 is a cross-sectional view of a fuel cell compressor system inaccordance with another embodiment of the present invention.

FIG. 4 is a cross-sectional view of a fuel cell compressor system inaccordance with another embodiment of the present invention.

FIG. 5 is a cross-sectional view of a seal system for a fuel cellcompressor system in accordance with another embodiment of the presentinvention.

FIG. 6 is a cross-sectional view of a fuel cell compressor systemincluding a seal system in accordance with another embodiment of theinvention.

FIG. 7 is a cross-sectional view of a fuel cell compressor systemincluding a seal system in accordance with another embodiment of theinvention.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction with theembodiments, it will be understood that they are not intended to limitthe invention to these embodiments. On the contrary, the invention isintended to cover alternatives, modifications and equivalents, which maybe included within the spirit and scope of the invention as embodied inor defined by the appended claims.

FIG. 1 generally illustrates a cross-sectional view of a fuel cellcompressor system 10 in accordance with an embodiment of the invention.The illustrated system 10 is shown including a motor 12, a drive housing14, a first gear set 16, carrier torque tube 18, first bearing 20, asecond gear set 22, impeller 24, and a second bearing 26. Embodiments ofthe system, of the type shown in FIG. 1, are sometimes referred to as“single-stage” compressor systems.

In the illustrated embodiment, motor 12 is shown connected to orincluding a motor shaft 28. Motor 12 may comprise an electric motor thatis provided to drive shaft 28. Further, one or more bearings (not shown)may be disposed within or about motor 12 for accommodating rotationalmovement of shaft 28. As illustrated, shaft 28 may extend in a generallyaxial direction. In an embodiment, motor 12 may comprise a low-speedmotor, although a high compressor speed may still be maintained throughuse of the system. A low speed motor may be considered to have a maximumoperating speed of no more than about 25,000 rpm.

A drive housing 14 can be provided to house one or more gear sets ofsystem 10 when gear sets are used in place of a direct drive system.Drive housing 14 at least partially surrounds motor shaft 28 and, inembodiments, one or more housing components may be configured tosubstantially enclose the entire motor shaft 28.

First gear set 16 is driven by motor shaft 28 and is configured to drivecarrier torque tube 18. In an embodiment, first gear set 16 may comprisea planet gear carrier, for example as generally illustrated in FIG. 1,such that motor shaft 28 is configured to drive a planet gear carrier.In another embodiment, first gear set 16 may comprise one or more spurgears, for example as generally illustrated in FIG. 2, such that motorshaft 28 is configured to drive a spur gear.

A carrier torque tube 18 can be provided to, among other things, atleast partially support motor shaft 28. The carrier torque tube 18 canbe configured to be driven by first gear set 16. In some embodiments,such as generally shown in FIG. 1, carrier torque tube 18 may beconnected or attached directly to first gear set 16, which may comprisea planet gear carrier. In another embodiment, carrier torque tube 18 maybe configured to be driven by a spur gear. In embodiments, the carriertorque tube 18 can be configured to rotate at a first (i.e., rotational)speed, which may be or correspond to motor speed.

A first bearing 20 or a plurality of bearings may be provided togenerally support carrier torque tube 18. First bearing 20 may includean outer race and an inner race. In an embodiment, two bearings may beprovided to generally support carrier torque tube 18, although fewer oradditional bearings may be provided and remain within the spirit andscope of the invention. In the illustrated embodiment, first bearing 20is disposed between carrier torque tube 18 and drive housing 14. Thefirst bearing 20 may also rotate at a first speed, like the carriertorque tube 18. In an embodiment, such first speed may be or correspondto motor speed. For some embodiments, first bearing 20 may comprise asealed greased bearing.

A second gear set 22 may be configured to be driven by the motor shaftand may be configured to drive impeller 24. In an embodiment, secondgear set 22 may comprise a planet gear 22 a, a ring gear 22 b, and a sungear 22 c. An example of such an embodiment is generally shown inFIG. 1. In the illustrated embodiment motor shaft 28 is configured todrive a planet gear carrier. Ring gear 22 b, which is fixed to drivehousing 14, permits sun gear 22 c to be driven faster than motor shaft28. In another embodiment, such as generally illustrated in FIG. 2,second gear set 22 may comprise one or more helical gears or spur gears.Gear set 22 is configured to drive impeller 24. In such an embodiment,the imposed axial force from the helical gear or spur gear of secondgear set 22 can oppose the natural axial force applied from impeller24—due at least in part to the pressure difference between the front andrear side of impeller 24. Accordingly, the axial forces from the secondgear set 22 and from the impeller 24 can be used to help balance eachother, which can reduce the loads on second bearing 26 and help toimprove the lifespan of second bearing 26.

The impeller 24 may rotate within a compressor to pressurize a fluidthat is flowing through system 10. The compressor may be connected tomotor 12 through any coupling or other methodology that is conventionalin the art. Only one impeller 24 is typically provided in a single-stagecompressor such as that generally illustrated in FIG. 1. However, asgenerally illustrated in FIG. 3, more than one impeller 24, 25 may beprovided in connection with multi-stage compressor systems. With amulti-stage compressor, fluid can be compressed to a first pressure in afirst stage and then further compressed to a higher pressure in a secondsequential stage. Referring again to FIG. 1, impeller 24 is generally atleast partially surrounded by a housing (not shown). Impeller 24includes or is connected to an impeller shaft 30. Impeller shaft 30 isconfigured to be driven by second gear set 22. In an embodiment, such asgenerally shown in FIG. 1, impeller shaft 30 may be driven by a sun gear22 c. Accordingly, impeller shaft 30 may be configured to rotate at asecond speed. This second speed may be greater than motor speed. Inanother embodiment, impeller shaft 30 may be configured to be driven byhelical gears or spur gears. In the latter embodiment, impeller shaft 30may still be configured to rotate at a second speed that may be greaterthan motor speed. Because impeller 24 (e.g., as shown in FIG. 1) orimpellers 24, 25 (e.g., as shown in FIG. 3) may be connected or attachedto impeller shaft 30, impellers 24 and 25 may both rotate at the speedof impeller shaft 30.

A second bearing 26 or a plurality of bearings can be provided to, amongother things, at least partially support impeller shaft 30. In anembodiment, two bearings may be provided to generally support carriertorque tube 18, although fewer or additional bearings may be providedand remain within the spirit and scope of the invention. In theillustrated embodiment, second bearing 26 is disposed between impellershaft 30 and carrier torque tube 18. With embodiments of the invention,second bearing 26 may rotate at the difference between motor speed andimpeller shaft speed. This difference may be dependent upon the gearratio of the second gear set 22, such as the gear ratio of the planetarysystem in FIG. 1. Second bearing 26 may include an outer race and aninner race. The rate of rotation of the outer race may be atsubstantially the same speed as the rate of rotation of the carriertorque tube 18. The rate of rotation of the inner race may be at leastpartially offset by the rate of rotation of the outer race because thecarrier torque tube 18 and the impeller shaft 30 may rotate in the samedirection. In other words, since the carrier torque tube 18 and theimpeller shaft 30 are both rotating in the same direction, thedifferential speed of the outer race of the second bearing 26 (e.g.,rotating at the same rate as the carrier torque tube 18) and the innerrace of the second bearing 26 (e.g., rotating at the same rate as theimpeller shaft 30) is less than if the carrier torque tube 18 were notincluded. In accordance with an embodiment of the invention, the secondbearing 26 may be rated to a lower manufacturing specification becausethe inner race may only need to be capable of rotation corresponding tothe difference between the rate of rotation of the carrier torque tube18 and the impeller shaft 30, rather than corresponding to the higherspeed of the rotation of the impeller shaft 30, which rotates at a speedgreater than motor speed. For some embodiments, the second bearing 26may comprise a sealed greased bearing.

In an embodiment as shown in FIG. 2, bearing losses may be mitigatedthrough a feedback loop through gear set 16. In particular, a torquepath may be created through gear set 22 and through bearing 26. Lossesassociated with bearing 26 may cause a force that is applied to gear set16 which may feed back into shaft 28, thereby regaining some of theenergy otherwise lost.

Referring to FIG. 2A, another embodiment of a fuel cell compressorsystem 210 in accordance with the principles of the invention isillustrated. Illustrated system 210 is substantially similar topreviously illustrated system 10, but includes modification to, amongother things, remove the gear set driving carrier torque tube 18. Asgenerally illustrated in the embodiment shown in FIG. 2A, system 210includes a gear set 222 that may drive impeller shaft 30. Bearing 26 forsupporting impeller shaft 30 may have some inherent drag that may resultin a force at the outer race of bearing 26 which may then be exerted oncarrier torque tube 18. Carrier torque tube 18 is supported at least inpart, by bearing 20 that enables rotation of carrier torque tube 18.Although no gear set is used to drive carrier torque tube 18, the forceexerted on carrier torque tube 18 from the shaft bearing 26 running dragmay cause carrier torque tube 18 to rotate. The total impeller shaft 30speed may be divided between bearing 26 supporting impeller shaft 30 andbearing 20 supporting carrier torque tube 18, which may prevent bearings20, 26 from overspeeding. For some embodiments, bearings 20, 26 maycomprise sealed greased bearings.

Referring to FIG. 2B, another embodiment of a fuel cell compressorsystem 310 in accordance with the principles of the invention isillustrated. Illustrated system 310 is substantially similar topreviously illustrated system 210, but includes modification to, amongother things, remove the gear set driving impeller shaft 30. Asgenerally illustrated in the embodiment shown in FIG. 2B, system 310includes impeller shaft 30 that is direct driven by motor 12. Motor 12may comprise either a low-speed motor (e.g., a motor with maximumoperating speed of no more than about 25,000 rpm) or a high-speed motor(e.g., a motor with operating speed greater than about 25,000 rpm, andin one embodiment with operating speed of about 60,000 rpm to about100,000 rpm). Bearing 26 may support impeller shaft 30 and may bemounted to carrier torque tube 18. Carrier torque tube 18 may besupported at least in part, by bearing 20 that may be mounted to thecompressor housing 314. Bearing 26 for supporting impeller shaft 30 mayhave some inherent drag that may result in a force at the outer race ofbearing 26 which may then be exerted on carrier torque tube 18. Theforce exerted on carrier torque tube 18 from the shaft bearing 26running drag may cause carrier torque tube 18 to rotate. The totalimpeller shaft 30 speed may be divided between bearing 26 supportingimpeller shaft 30 and bearing 20 supporting carrier torque tube 18,which may prevent bearings 20, 26 from overspeeding. For someembodiments, bearings 20, 26 may comprise sealed greased bearings.

Referring to FIG. 4, another embodiment of a fuel cell compressor system110 in accordance with principles of the invention is illustrated.Illustrated system 110 is substantially similar topreviously-illustrated system 10, but includes modifications to, amongother things, allow for a multi-stage compressor with two impellers thatcan operate at different speeds. As generally illustrated in theembodiment shown in FIG. 4, system 110 may comprise a first impeller 124and a second impeller 125. First impeller 124 can be configured forrotation within a compressor to pressurize a fluid that is flowingthrough a first stage of system 110. First impeller 124 may be connectedor attached to carrier torque tube 18. Accordingly, first impeller 124may rotate at a first speed that corresponds to or is the same as thatof carrier torque tube 18. In an embodiment, carrier torque tube andfirst impeller 124 may rotate at or correspond to motor speed.

Second impeller 125 can be configured for rotation within a compressorto further pressurize a fluid that is flowing through a second stage ofsystem 110. Second impeller 125 may be connected or attached to impellershaft 30. Impeller shaft 30 can be configured to be driven by the secondgear set 22. As generally illustrated in connection with the embodimentshown in FIG. 4, impeller shaft 30 may be configured to be driven by asun gear 22 c. Accordingly, impeller shaft 30 may be configured torotate at second speed. Second impeller 125 may rotate at a second speedthat is the same as that of impeller shaft 30. In an embodiment,impeller shaft 30 and second impeller 125 may be configured to rotate ata speed greater than motor speed. The second speed may be greater thanthe first speed at which first impeller 124 rotates. Accordingly, firstimpeller 124 and second impeller 125 can be configured so as to be ableto operate at different speeds in system 110, which can provide moreflexibility with respect to fluid delivery.

In an embodiment, system 110 may further include a clutch 100. Clutch100 can be provided and configured to permit ring gear 22 b to slip,and/or controllably slip, so that the power delivered to second impeller125 may be modified for changed fluid flow. Clutch 100 may, for example,be disposed between drive housing 14 and ring gear 22 b of second gearset 22. As illustrated, ring gear 22 b may be disposed between impellershaft 30 and drive housing 14. Moreover, in an embodiment, system 110may further include a diverter, such as diverter valve 102. A divertervalve 102 may be configured and provided to permit fluid to bypass asecond stage of system 110. Disengaging and bypassing the second stageof system 110 may provide for more efficient operation of system 110,for example, when full compressor output may not be desired or required.

Embodiments of the systems, such as illustrated systems 10 and 110, mayfurther include a seal system for reducing or preventing contaminationof fluid in the system. A seal system may be provided to, among otherthings, reduce or eliminate contamination of the fluid in systems by oilthat may be used to lubricate gears associated with embodiments of thesystem. Referring to FIGS. 5-6, the seal system may include, by way ofexample and without limitation, a first seal 32, a second seal 34, and adrain 36.

As generally shown in the illustrated embodiment, a first seal 32 may beprovided to prevent contaminants, such as oil from migrating from drivehousing 14 to the compressor. Such a first seal 32 may include a borethat is closely toleranced to match or correspond to the impeller shaft30. In other words, for some embodiments a small running clearance maybe provided between first seal 32 and shaft 30. First seal 32 may, forinstance, be disposed around impeller shaft 30 proximate impeller 24 or124. A first side 38 of first seal 32 can be pressurized to thecompressor pressure, while a second side 40 of first seal 32 can bevented to atmosphere, thereby creating a pressure gradient. Such apressure gradient may be used to help prevent contaminants, such as oil,from migrating past first seal 32 and may also prevent air leaks, whichwould decrease the efficiency of systems 10 and 110. First seal 32 maycomprise any dimensionally stable material suitable for such anenvironment. In an embodiment, first seal 32 may comprise, for example,phenolics, ceramic, glass, or silicon nitride. Although these materialsmay be described in some detail or with some specificity, it isunderstood by those of ordinary skill in the art that numerous othermaterials may be used for first seal 32 and remain within the spirit andscope of the invention.

In an embodiment, a second seal 34 may be provided as part of adouble-seal arrangement for the seal system. As generally illustrated,second seal 34 may be included and disposed around impeller shaft 30between first seal 32 and the gear system. The second seal 34 maycomprise a rubber. Although rubber is specifically noted, it isunderstood by those of ordinary skill in the art that numerous othermaterials may be used for second seal 34 and remain within the spiritand scope of the invention.

As further generally shown in the illustrated embodiment, a drain 36 maybe included and disposed in drive housing 14 between first seal 32 andsecond seal 34. The drain 36 may be used for draining contaminants fromthe system. In an embodiment, drain 36 may drain leaked oil outside theseal system so that it does not contaminate fluid within the system.

The seal system may further include a device or means for forcing atleast a portion of first seal 32 against drive housing 14. For example,as generally illustrated in the depicted embodiment, a wave spring 42may be provided to force at least a portion of first seal 32 againstdrive housing 14. The use of such a device or means may help prevent oilmigration around the outside of first seal 32 and may prevent rotationof the first seal 32. Each of the embodiments illustrated in FIGS. 1-4may be modified to include a seal system as shown generally in FIG. 5,for example. An exemplary modification to the fuel cell compressorembodiment illustrated in FIG. 1 to include a seal system is generallyillustrated in FIG. 6. The seal system may comprise first seal 32, asecond seal 34, and a drain 36. In accordance with an embodiment of theinvention, the first seal 32 and second seal 34 may both be disposedbetween the impeller shaft 30 and the drive housing 14. Drain 36 may bedisposed in the drive housing 14 between first seal 32 and second seal34. The seal system may further include a wave spring 42 disposedbetween the first seal 32 and second seal 34. Other configurations for aseal system for use in connection with various embodiments of the fuelcell compressor system are apparent to those of ordinary skill in theart. For example, as generally illustrated in FIG. 7, the seal systemmay comprise first seal 44, second seal 46, and a drain 48. The firstseal 44 may be disposed between the impeller shaft 30 and the carriertorque tube 18, and the second seal 46 may be disposed between thecarrier torque tube 18 and the drive housing 14. In such an arrangement,the first and second seals 44, 46 may be capable of a lower rate ofspeed than if both seals were disposed between the impeller shaft 30 andthe drive housing 14. This is because the relative speed between thecarrier torque tube 18 and the impeller shaft 30 and the relative speedbetween the carrier torque tube 18 and the drive housing 14 are lowerthan the relative speed between the impeller shaft 30 and the drivehousing 14. Drain 48 may generally be smaller than drain 36. Drain 48may be small enough in an embodiment such that even if air was to leak,it may not be enough to cause a noticeable change in performance. Anyoil that may leak past seals 44,46 may be forced out drain hole 48.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and various modifications andvariations are possible in light of the above teaching. The embodimentswere chosen and described in order to explain the principles of theinvention and its practical application, to thereby enable othersskilled in the art to utilize the invention and various embodiments withvarious modifications as are suited to the particular use contemplated.It is intended that the scope of the invention be defined by the claimsappended hereto and their equivalents.

1. A fuel cell compressor system, comprising: a motor, including a motor shaft driven by the motor; a drive housing at least partially surrounding the motor shaft; a first gear set driven by the motor shaft; a carrier torque tube driven by the first gear set, the carrier torque tube configured to rotate at motor speed; a second gear set driven by the motor shaft; and an impeller, including an impeller shaft driven by the second gear set, the impeller shaft configured to rotate at a speed greater than motor speed.
 2. A system in accordance with claim 1, including a first bearing disposed between the tube and the drive housing for at least partially supporting the tube, and a second bearing disposed between the impeller shaft and the tube for at least partially supporting the impeller shaft.
 3. A system in accordance with claim 1, wherein the first gear set comprises a spur gear or a planet gear carrier.
 4. A system in accordance with claim 1, wherein the second gear set comprises a helical gear or a spur gear.
 5. A system in accordance with claim 2, wherein the second bearing includes an outer race and an inner race, wherein the rate of rotation of the outer race is at substantially the same speed as the rate of rotation of the carrier torque tube.
 6. A system in accordance with claim 5, wherein the rate of rotation of the inner race is at least partially offset by the rate of rotation of the outer race.
 7. A system in accordance with claim 2, wherein the carrier torque tube and the impeller shaft rotate in the same direction.
 8. A system in accordance with claim 2, wherein the first bearing comprises a sealed greased bearing.
 9. A system in accordance with claim 2, wherein the second bearing comprises a sealed greased bearing.
 10. A system in accordance with claim 1, wherein the motor comprises a low-speed motor.
 11. A system in accordance with claim 2, wherein the first bearing rotates at motor speed.
 12. A system in accordance with claim 2, wherein the second bearing rotates at the difference between motor speed and impeller shaft speed.
 13. A system in accordance with claim 1, further comprising a seal system for preventing contamination of fluid in the system
 14. A system in accordance with claim 13, wherein the seal system is disposed between the impeller shaft and the drive housing.
 15. A system in accordance with claim 13, wherein the seal system is disposed between the impeller shaft and the carrier torque tube.
 16. A system in accordance with claim 13, wherein the seal system is disposed between the carrier torque tube and the drive housing.
 17. A system in accordance with claim 13, wherein the seal system comprises: a first seal; a second seal; and a drain located in the drive housing for draining contaminants from the system.
 18. A system in accordance with claim 17, wherein the drain is located between the first seal and the second seal.
 19. A system in accordance with claim 17, wherein a first side of the first seal is pressurized and a second side of the first seal is vented to the atmosphere, thereby creating a pressure gradient.
 20. A system in accordance with claim 17, further comprising a wave spring for forcing the first seal against the drive housing.
 21. A system in accordance with claim 17, wherein the first seal comprises one of phenolics, ceramics, glass, or silicon nitride.
 22. A system in accordance with claim 17, wherein the second seal comprises rubber.
 23. A fuel cell compressor system, comprising: a motor, including a motor shaft driven by the motor; a drive housing at least partially surrounding the motor shaft; a first gear set driven by the motor shaft; a carrier torque tube driven by the first gear set, the carrier torque tube configured to rotate at a first speed; a first bearing disposed between the carrier torque tube and the drive housing for at least partially supporting the tube; a first impeller driven by the carrier torque tube at a first speed for imparting fluid flow through a first stage of the system; a second gear set driven by the motor shaft; an impeller shaft driven by the second gear set, the impeller shaft configured to rotate at a second speed; and a second bearing disposed between the impeller shaft and the tube for at least partially supporting the impeller shaft. a second impeller driven by the impeller shaft at a second speed for imparting fluid flow through a second stage of the system.
 24. A system in accordance with claim 23, further comprising a diverter valve configured to allow fluid to bypass the second stage of the system.
 25. A system in accordance with claim 23, wherein the second speed is greater than the first speed.
 26. A system in accordance with claim 23, wherein the first bearing and second bearing include sealed greased bearings.
 27. A fuel cell compressor system, comprising: a motor, including a motor shaft driven by the motor; a gear set driven by the motor shaft, the gear set disposed within a drive housing at least partially surrounding the motor shaft; an impeller, including an impeller shaft driven by the motor shaft wherein the impeller shaft is configured to be driven by the gear set at a speed greater than motor speed; a compressor housing surrounding the impeller; a carrier torque tube at least partially surrounding the motor shaft; a first bearing disposed between the impeller shaft and the carrier torque tube for at least partially supporting the impeller shaft; a second bearing disposed between the carrier torque tube and the compressor housing for at least partially supporting the carrier torque tube, wherein the first and second bearings are each configured to rotate at a speed less than motor speed. 